I have a pair of old Specialized trispoke wheels, first generation carbon composite, which I've adopted for track use. I have the opportunity to pick up an older HED disc for about $100, and I can use the same over-priced track adapter kit which I bought for use on the Specialized on the HED disc, then probably just sell the trispoke on eBay for a quick few hundred.
I am a strong mass-start racer, and not a pursuit specialist or someone who really excels at any of the individual effort races, so it is not as though I need it to shave a precious fraction of a second off somewhere. I'd imagine the the nature of the materials (solid carbon composite vs. hollow carbon walls) would make the trispoke some measure stiffer, which might benefit me more than a disc, but we all know that the disc is inherently more aerodynamic, and probably stiff enough for my 130lbs self.
So if you had to choose one or the other, would you have an old flexy trispoke wheel or an old flexy HED disc? This is for use at an outdoor velodrome, by the way.